Chain homogeneity and thermo-mechanical behaviour of polyphosphazenes. Synthesis of the random copolymers {[NP(O2C12H8)1−x[NP(OCH2CF3)2]x}n

The phosphazene homo and copolymers combining the λ5-phosphorus-dioxy-biaryl units [NP(O2C12H8)] or {[NP(O2C20H12)]n (O2C12H82,2′-dioxy-1,1′-biphenyl, O2C20H12 = R or R/S-2,2′-dioxy-1,1′-binaphthyl) and the conventional units [NP(OC6H4CO2Pr)2] or [NP(OCH2CF3)2], including the new series {[NP(O2C12H8)]1−x[NP(OCH2CF3)2]x}n (x = 0-1), all prepared by alkali carbonate assisted sequential macromolecular substitution from [NPCl2]n have been studied by DSC-assisted thermo mechanical analysis. The results showed that the thermal expansion coefficient changes in dilatation mode and the softening temperature in the compression mode are coincident with the glass transition temperatures (Tg) as measured by DSC except for the random copolymers containing the λ5-phosphorus-dioxy-biaryl units in the approximate interval 40-60% for which the softening temperatures were much higher. For the chiral polymers with [NP(O2C20H12)]n units, the TMA differences between the isomers R, R/S and the atactic products formed by their thermal atropisomerisation near the Tg suggest that the R/S product resulting in the macromolecular substitution from [NPCl2]n and rac-binaphthol may have some degree of tacticity.